(1) Field of the Invention
The present invention relates to a device for cutting and forming a lead frame of a semiconductor device, which is used in a manufacturing process of the semiconductor device.
(2) Description of the Related Art
A conventional cutting and forming device of the kind to which the present invention relates is explained with reference to the appended drawings. FIG. 1 is a diagrammatic view of such conventional cutting and forming device. FIG. 2A is a diagrammatic view showing the relation in locations of a die 5 of the device and a semi-finished product 10 molded in resin, in a state where the latter is being forwardly fed, and FIG. 2B is a diagrammatic view showing the relation in locations of the die 5 and the semi-finished product 10 in a state in which the die 5 is at its bottom dead point.
As shown in FIG. 2B, as the die 5 is provided with a relief or recess portion having a sufficient depth so as to give a slight relief for a bottom surface of the semi-finished product 10, the lead frames 3 are allowed to be in contact with the upper surface of the die 5 while a cutting and forming process is actually performed. As shown in FIG. 2A, when the lead frames 3 are to be fed forwardly, they are lifted up by a lifting mechanism to an extent larger than the thickness of a resin portion of the semi-finished product 10 (approximately 5 mm as shown by "A" in the drawings). Such lifting mechanism lifts up an entire feeding rails 4 as shown in FIG. 1. The feeding rail 4 is carried by guide posts provided on a lower die base 6 and is pressed up by spring means.
Such conventional cutting and forming device includes, as a press mechanism, an upper die base 1, a punch 11 and a stripper frame 2. The downward operation of the press mechanism accompanies noise which is produced mainly at a point when the stripper frame 2 strikes or abuts against the feeding rail 4 and at a point when the stoppers provided in the upper and lower die bases strike against each other at the bottom dead point of the press ram. In order to reduce noise of such kinds, it is necessary that the speed of the press operation at the above two points be decelerated. For doing so, a means employed is to have the press mechanism driven by a servo-motor and have the speed of the motor controlled so as to decelerate the speed of the downward movement of the press mechanism. FIG. 3 shows, with a press mechanism having a speed deceleration function in the vicinity of the bottom dead point of the press ram as an example, the relation between ram changes and press ram speeds obtained by a crank driven mechanism. It is seen therein that the ram speeds are controlled so that they are decelerated along a curve and reach the bottom dead point.
In the conventional cutting and forming device as explained above, as shown in FIG. 1, the stripper frame 2 of the upper die base 1 in its downward movement presses down the feeding rails 4 so that the position at which stripper frame 2 abuts on the feeding rails 4 is about 7 mm above the bottom dead point, the value being the sum of 5 mm which is the relief (shown by "A" in FIG. 2A) for the thickness of the resin molding portion of the semi-finished product 10 and 2 mm which is the amount of the movement of the punch 11 thrusting into the die 5 in the lead cutting operation.
Also, in the upward movement of the press ram which takes place when the feeding rail and the stripper frame restore to their initial states they are stopped suddenly by their stoppers thereby producing noise. This develops at the position about 5-7 mm above the bottom dead point. Thus, in the upward movement of the press ram also, it is necessary that the speed of the press ram movement be decelerated. This state is shown by a timing chart in FIG. 7A from which it is noted that, at the point at which the feeding rails 4 and the stripper frame 2 abut with their stoppers, the upward and downward speeds of the press ram are decelerated.
In the conventional device, it was necessary that, in order to reduce noise of various kinds, the speeds of the press ram should be decelerated at a plurality of points as explained above, which presented the problem that a time necessary for one-shot operation unavoidably became long. This problem in the conventional device is to be solved by the invention.